On Time Delivery calculation

Hi All,

How can i to write the coding as below expectation:

Conditions:
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a.) Shedule Ship Date - Actual Shipment > 0 Then "Failded OTD"

b.) Shedule Ship Date - Actual Shipment <= 0 Then "Pass OTD OTD"

c.)  If actual shipment date is null, then "Not Yet Deliver"

d.) Days variance : Shedule Ship Date - Actual Shipment

SQL Command: 
----------------------

SELECT
case when (trunc(schedule_ship_date) - to_date(ool.actual_shipment_date,'DD-MON-YY')) < 0 then 'FAILED'
                      else 'PASS' end as "OTD"
 ,trunc(schedule_ship_date) - to_date(ool.actual_shipment_date,'DD-MON-YY') "DAYS VARIANCE"
From  oe_order_lines_all ool